Add user-agent to all http requests initiated by Workhorse

workhorse/internal/api/api.go

workhorse/internal/dependencyproxy/dependencyproxy.go

workhorse/internal/imageresizer/image_resizer.go

workhorse/internal/sendurl/sendurl.go

workhorse/internal/transport/transport.go

workhorse/internal/upload/destination/objectstore/object.go

workhorse/internal/version/version.go

workhorse/internal/version/version_test.go

workhorse/internal/zipartifacts/open_archive.go

workhorse/main.go